WEE1 inhibition triggers GCN2-mediated activation of the integrated stress response

The WEE1 kinase negatively regulates the CDK1/2 kinases to control DNA replication and prevent premature entry into mitosis. Pharmacological inhibition of WEE1 (WEE1i) causes hyperactivation of CDK1 and CDK2, leading to premature mitosis in the presence of DNA lesions. WEE1i treatment is particularly cytotoxic in cells with oncogene-induced or treatment-induced replication stress. To uncover genetic factors that sensitize cancer cells to WEE1i, a genome-wide insertional mutagenesis screen was performed and identified that mutation of the alternative translation initiation factor EIF2A sensitized cells to WEE1i. WEE1i sensitivity of EIF2AKO cells was not explained by altered replication kinetics. Rather, WEE1i leads to a translational shut-down which is lethal in combination with the reduced translation in EIF2AKO cells. A genome-wide CRISPR-Cas9 screen in WEE1i-treated cells revealed that inactivation of the integrated stress response (ISR) kinase GCN2 rescued WEE1i-mediated cytotoxicity. In line with these findings, WEE1i resulted in GCN2 activation, ATF4 upregulation and a translational shutdown. Moreover, WEE1 inhibition leads to altered ribosome dynamics and increased ribosome collisions. Accordingly, cells lacking the collided ribosome sensor ZNF598 show increased sensitivity to WEE1i. This response was not restricted to cancer cells, but was also observed in peripheral blood monocytic cells. The GCN2-mediated ISR was not required for WEE1i to induce DNA damage in S-phase, premature mitotic entry nor the sensitizing effects to DNA damaging chemotherapeutics. Conversely, ISR activation and translational shut-down are independent on WEE1i-mediated activation of CDK1/2. WEE1i-mediated ISR activation was independent of the presence of WEE1, pointing at an off-target effect, which is shared by multiple chemically distinct WEE1 inhibitors. Importantly, WEE1 inhibition at doses that do not induce the ISR can still synergize with PKMYT1 inhibition. Taken together, pharmacological WEE1 inhibition triggers cytotoxic ISR activation and translational shutdown, which can be prevented by low-dose treatments, while retaining the cell cycle checkpoint-perturbing effects.